HARTFORD, Conn. — Adam Lanza’s parents and educators contributed to his social isolation in the years before he carried out the 2012 Sandy Hook Elementary School massacre by accommodating — and not confronting — his difficulties engaging with the world, according to a state report issued Friday.

The Office of the Child Advocate, which investigated Lanza’s upbringing to glean lessons for preventing future tragedies, concluded that Lanza’s parents, education team and others missed signs of how deeply troubled he was and missed opportunities to steer him toward more appropriate treatment.

Lanza killed his mother, then shot his way into the Newtown school Dec. 14, 2012, and gunned down 20 children and six educators before killing himself.

In exploring what could have been done differently, the new report homed in on his mother, Nancy Lanza, who backed her son’s resistance to medication and, from 10th grade on, kept him at home, where he was surrounded by an arsenal of firearms and spent long hours playing violent video games.

“Mrs. Lanza’s approach to try to help him was to actually shelter him and protect him and pull him further away from the world, and that in turn turned out to be a very tragic mistake,” Julian Ford, one of the report’s authors, said at a news conference.

The authors said Lanza’s parents tried to obtain help for him, but they did not know which path to take.

The one provider that seemed to understand the gravity of his condition, the Yale Child Study Center, evaluated him in 2006 and called for rigorous daily therapy and medication for conditions such as anxiety.

At the time, a Yale psychiatrist warned there was risk to creating a “prosthetic environment which spares him having to encounter other students or to work to overcome his social difficulties,” according to the report.

After the evaluation, Nancy Lanza told the doctor by e-mail that her son would not agree to any sort of medication and that he had been angered by the doctor’s line of questioning. The Yale recommendations went unheeded.

Joseph Erardi Jr., the superintendent of schools for Newtown, said the report will have great meaning if “there is one school leader, one district, one mental health provider or one set of parents who reads this work and can prevent such a heinous crime.”

The Larimer County coroner on Sunday performed an autopsy on the body found on a farm just east of Loveland Saturday, but the office will not release the cause of death or the identity of the person until they can track down next of kin.